The investigation is looking into allegations that Progress Rail Services may have violated environmental law and taken part in improper business practices. Reuters

California federal prosecutors are investigating Progress Rail Services Corp., a unit of Caterpillar Inc.

Announced by the company in a regulatory filing on Friday, the investigation will look into the subsidiary’s possible violations of environmental law as well potential improper business practices, reports Reuters. Based in Peoria, Ill., Caterpillar said Progress Rail received a grand jury subpoena from the U.S. District Court for the Central District of California on Oct. 24.

Documents and other information from Progress Rail, Caterpillar and Progress Rail subsidiary United Industries Corp. were requested in the subpoena. The files are in relation to Progress Rail having allegedly lead improper or unneeded rail inspections. The filing also said the company improperly disposed of equipment, tools, parts and other items.

According to the statement, Caterpillar is cooperating with investigators.